1. Field of the Invention
The present invention relates to an apparatus and method for judging road surface gradients as well as to a program for judging gradients. More particularly, it relates to an apparatus and method for judging road surface gradients and a program for judging gradients for judging gradients of the road surface on which the vehicle is running to thereby improve running performances.
2. Description of Background Art
Control is conventionally performed in a vehicle equipped with, for instance, an automatic transmission, that gear shifts on a high speed side of the automatic transmission are limited for improving dynamic performances when running uphill or that the gear shifts on the high speed side of the automatic transmission are limited for improving engine braking performances when running downhill. A road surface gradient detecting device for detecting gradients of the road surface on which the vehicle is running is employed for such control.
It is the case with conventional devices that accelerator openings and front and rear accelerations of the vehicle are respectively detected for determining that the vehicle is running uphill in case the accelerator opening is not less than a specified opening and in case the acceleration in front and rear directions of the vehicle is not more than a specified level.
However, since the above method is not sufficient to accurately obtain gradients, there has been proposed in, for instance, Japanese Unexamined Patent Publication No. 145323/1992, a road surface gradient detecting device (A) for obtaining a gradient of the road surface on which the vehicle is running based on a difference between acceleration in front and rear directions of the vehicle as obtained through detection signals of a front and rear acceleration sensor mounted on the vehicle and running acceleration which is indicative of changes per unit times for the vehicle speed as obtained through pulse signals of a vehicle speed sensor. Such a device A is capable of detecting gradients of a road surface by diverting the front and rear acceleration sensor which is provided for suspension control, and upon utilizing detected gradients of the road surface as transmission control information for the automatic transmission, it is possible to improve controllability of transmission.
Japanese Unexamined Patent Publication No. 242862/1997 further describes a road surface gradient estimating apparatus (B). In this publication, it is made use of a relation given by vehicle driving torque=resistance torque when running on a flat road+acceleration resistance torque+gradient resistance torque, since a vehicle driving torque balances with a sum of resistance torque when running on a flat road, an acceleration resistance torque, and a gradient resistance torque. It is recited therein that the gradient resistance torque can be obtained upon obtaining the vehicle driving torque, the resistance torque when running on a flat road, and the acceleration resistance torque, so that it is possible to calculate a road surface gradient sin xcex8 from the following equation:
Txcex8=Wxc3x97Gxc3x97sin xcex8xc3x97Rt
Here, T xcex8: gradient resistance torque
W: vehicle weight
G: gravitational acceleration
Rt: dynamic radius of tire
While a conventional apparatus as disclosed in Japanese Unexamined Patent Publication No. 147304/1994 does not take it into consideration that acceleration resistance torque is changed in accordance with gear ratio, it is stated that the above apparatus B performs calculation of acceleration resistance torque even more accurately upon considering the gear ratio for accurately obtaining gradients of the road surface.
However, when using a front and rear acceleration sensor for detecting gradients of a road surface, the structure of a control circuit will become complicated which, in turn, leads to increased costs owing to the fact that a detection sensor is additionally required besides detectors related to an ABS device. Also in case gradients are obtained by using an acceleration sensor or on the basis of vehicle speed without using an acceleration sensor, it is difficult to accurately calculate the acceleration resistance torque.
In view of the above facts, it is an object of the present invention to provide an apparatus and method for judging road surface gradients and a program for judging gradients of the road surface on which a vehicle is running to thereby improve running performances through a simple structure.
In accordance with the present invention, there is provided an apparatus for judging road surface gradients including a speed detecting means for periodically detecting wheel speeds of four wheels of a vehicle, a vehicle body speed calculating means for obtaining a vehicle body speed of the vehicle, a slip rate calculating means for obtaining a slip rate, a means for calculating acceleration of the vehicle body for obtaining an acceleration of the vehicle body of the vehicle, a determining means for determining whether the acceleration of the vehicle body is within a specified range proximate to zero, and a gradient judging means for judging a gradient of a road surface on the basis of the determination of the determining means.
In accordance with the present invention, there is also provided a method for judging road surface gradients including the steps of: periodically detecting wheel speeds of four wheels of a vehicle, obtaining a vehicle body speed of the vehicle, obtaining a slip rate, obtaining an acceleration of the vehicle body of the vehicle, determining whether the acceleration of the vehicle body is within a specified range proximate to zero, and judging a gradient of a road surface on the basis of the determination.
Furthermore, in accordance with the present invention, there is further provided a program for judging gradients which makes a computer function as a vehicle body speed calculating means for obtaining a vehicle body speed of the vehicle, a slip rate calculating means for obtaining a slip rate, a means for calculating acceleration of the vehicle body for obtaining an acceleration of the vehicle body of the vehicle, a determining means for determining whether the acceleration of the vehicle body is within a specified range proximate to zero, and a gradient judging means for judging a gradient of a road surface on the basis of the determination of the determining means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.